Communications terminal and method of communicating

ABSTRACT

A communications terminal communicates data to/from a mobile communications network. The mobile communications network includes a radio network including one or more base stations configured to provide a low bandwidth communications interface formed from a low bandwidth carrier for communicating the data to or receiving the data from the communications terminal in accordance with a relatively low bandwidth, and to provide a high bandwidth communications interface formed from a high bandwidth carrier for communicating the data to or receiving the data from the communications terminal in accordance with a relatively high bandwidth. The communications terminal is configured to attach for communication to the high bandwidth interface, and in response to receiving a command from the mobile communications network, to detach from the high bandwidth interface and to re-attach to the low bandwidth interface for communicating the data to or from the mobile communications network via the low bandwidth interface.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is based on PCT filing PCT/GB2012/052354 filedSep. 24, 2012, and claims priority to British Patent Application1116898.6, filed in the UK IPO on Sep. 30, 2011 and British PatentApplication 1116902.6, filed in the UK IPO on Sep. 30, 2011, the entirecontents of each of which being incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to communications terminals forcommunicating data to and/or from mobile communications networks andmethods of communicating data to and receiving data from mobilecommunications networks.

BACKGROUND OF THE INVENTION

Mobile communication systems have evolved over the past ten years or sofrom the GSM System (Global System for Mobiles) to the 3G system and nowinclude packet data communications as well as circuit switchedcommunications. The third generation partnership project (3GPP) has nowbegin to develop a fourth generation mobile communication systemreferred to as Long Term Evolution (LTE) in which a core network parthas been evolved to form a more simplified architecture based on amerging of components of earlier mobile communications networkarchitectures and a radio access interface which is based on OrthogonalFrequency Division Multiplexing (OFDM) on the downlink and SingleCarrier Frequency Division Multiple Access (SC-FDMA) on the uplink. Thecore network components are arranged to communicate data packets inaccordance with an enhanced packet communications system.

Third and fourth generation mobile telecommunication systems, such asthose based on the 3GPP defined UMTS and Long Term Evolution (LTE)architecture are able to support more sophisticated services than simplevoice and messaging services offered by previous generations of mobiletelecommunication systems.

For example, with the improved radio interface and enhanced data ratesprovided by LTE systems, a user is able to enjoy high data rateapplications such as mobile video streaming and mobile videoconferencing that would previously only have been available via a fixedline data connection. Third and fourth generation mobile communicationnetworks therefore typically employ advanced data modulation techniqueson the radio interface which can require more complex and expensiveradio transceivers to implement. However not all communications are of anature which requires the full bandwidth capability of for example theLTE system.

The anticipated widespread deployment of third and fourth generationnetworks has led to the parallel development of a class of terminals andapplications which, rather than taking advantage of the high data ratesavailable, instead take advantage of the robust radio interface andincreasing ubiquity of the coverage area. Examples include so-calledmachine type communication (MTC) applications, which are typified bysemi-autonomous or autonomous wireless communication terminals (i.e. MTCterminals) communicating small amounts of data on a relativelyinfrequent basis. Thus the use of an MTC terminal may differ from theconventional “always-on” use case for conventional LTE terminals.Examples of MTC terminals include so-called smart meters which, forexample, are located in a customer's house and periodically transmitinformation back to a central MTC server data relating to the customer'sconsumption of a utility such as gas, water, electricity and so on. Inthe example of a smart meter, the meter may both receive small datatransmissions (e.g. new price plans) and send small data transmissions(e.g. new readings) where these data transmissions are generallyinfrequent and delay-tolerant. Characteristics of MTC terminals mayinclude for example one or more of: a low mobility of the communicationsterminal; highly specific time controlled transmissions; delay tolerantdata transmissions; transmissions which are packet switched (PS) only;transmissions of small amounts of data; mobile originated onlycommunications; infrequent mobile terminated communications. As suchtypical applications for MTC-type devices would be for examplemonitoring applications; priority alarm applications; secure connectioncommunications; communication of data dependent upon location specifictriggers; group based MTC features (for example: group based policingand group based addressing); vending machines; “sat nav” terminals; andsecurity cameras or sensors, etc.

It will therefore be appreciated that low bandwidth MTC-type terminalsmay be operating contemporaneously with conventional or legacy terminalswhich may require high bandwidth communications. Accordingly it isdesirable to improve the efficiency with which communications resourcesare used by a mobile communications network which is configured toprovide both low bandwidth communications and high bandwidthcommunications.

SUMMARY OF THE INVENTION

According to the present invention there is provided a communicationsterminal for communicating data to and receiving data from a mobilecommunications network. The mobile communications network includes aradio network part including one or more base stations configured toprovide a low bandwidth communications interface formed from a lowbandwidth carrier for communicating the data to or receiving the datafrom the communications terminal in accordance with a relatively lowbandwidth, and to provide a high bandwidth communications interfaceformed from a high bandwidth carrier for communicating the data to orreceiving the data from the communications terminal in accordance with arelatively high bandwidth. The communications terminal is configured toattach for communication to the high bandwidth interface, and inresponse to receiving a command from the mobile communications network,to detach from the high bandwidth interface and to re-attach to the lowbandwidth interface for communicating the data to or from the mobilecommunications network via the low bandwidth interface. Accordinglycommunications resources of the mobile communications network which areallocated for the low bandwidth interface may be used more efficientlyby load balancing between the low bandwidth interface and the highbandwidth interface.

Embodiments of the present invention can utilise communicationsresources of a mobile communications network which are allocated for alow bandwidth interface more efficiently. In one example, the one oremore communications terminals which are communicating data via the lowbandwidth interface belong to class of communications terminal, whichare configured only to communicate via the low bandwidth interface,because they do not have a capability for communicating via the highbandwidth interface. As such the load balancing entity is configured totransfer communications terminals attached to the high bandwidthinterface to the low bandwidth interface when the class of low bandwidthcommunications terminals are not utilising the communications resourcesavailable from the low bandwidth interface.

It is envisaged that a low bandwidth radio communications interface,which is also referred to as a low bandwidth carrier, may be provided bya mobile communications network for communicating data at a lowbandwidth to communications terminals. Furthermore these communicationsterminals may be provided with a transmitter and receiver that can onlycommunicate data via the low bandwidth interface. In one example theselow bandwidth communications terminals may be used to form MTC-typecommunications devices or configured for MTC type applications. Sincethe low bandwidth interface has been allocated communications resourceswhich may be difficult to re-allocate to be used by conventional higherbandwidth devices, a load balancing entity is provided to transferconventional devices on to the low bandwidth interface, underpredetermined conditions in order that the communications resourcesallocated to the low bandwidth interface can be more efficientlyutilised. Such predetermined conditions may include whether thecommunications resources allocated to the low bandwidth interface arebeing under utilised.

The number of communication terminals which are transferred may dependon the relative utilisation of both the high/bandwidth carrier and thelow bandwidth carrier. If a communication terminal, which is capable oftransmitting via the high bandwidth carrier, is attached to the lowbandwidth carrier and has significant data to transmit, it istransferred to the high bandwidth carrier. It is only the high bandwidthcapable devices like the smart-phones which were in DRX state on the lowbandwidth carrier which would be transferred to the high bandwidthcarrier.

In other examples the predetermined conditions for the load balancingentity to move communication terminals from the high bandwidth interfaceto the low bandwidth interface include, for example, whether thecommunication terminals are in some semi-dormant state, such as wherethey are only transmitting small signalling messages. Examples of suchstates include when the communications terminal has entered an idlestate or when the communications terminal has entered a state in whichit is discontinuously receiving from the network (DRX). In some examplesthe mobile communications network may instruct the communicationsterminal to enter the idle state or the discontinuous reception state,which may be instructed using a radio resource control (RRC) message. Assuch in some embodiments the RRC message, which instructs thecommunications terminal to enter idle state or the DRX state may beadapted to provide an indication that the communications terminal shoulddetach from the high bandwidth communications interface and attach tothe low bandwidth communications interface.

In other embodiments the mobile communications network may communicateto a communications terminal, which is commanded to detach from the highbandwidth interface and re-attach to the low bandwidth interface, abiasing condition for re-attaching to the high bandwidth interface fromthe low bandwidth interface to an effect that the communicationsterminal remains preferentially attached to the low bandwidth interface.As such, in order to reduce a likelihood of a communications terminalre-attaching to the high bandwidth interface from the low bandwidthinterface, because the high bandwidth interface has a higher receivedsignal strength, the communications terminal is biased to remainattached preferentially to the low bandwidth interface. As such, thecommunications terminal may still re-attach to the high bandwidthinterface, but for example, only where signal strength received from thelow bandwidth interface falls to an extent that the communication ofdata may be compromised. As a consequence a communications terminal inthe idle state can be moved to the low bandwidth carrier for loadbalancing and will then remain attached to the low bandwidth carrier,rather than re-attaching to the high bandwidth carrier.

The present application claims the Paris Convention priority toUK1116898.6 and UK1116902.6 filed 30 Sep. 2011, the contents of whichare incorporated herein by reference.

Further aspects and features of the present invention are defined in theappended claims and include a method of communicating data using acommunications terminal to and receiving data from a mobilecommunications network.

BRIEF DESCRIPTION OF THE DRAWINGS

Example embodiments of the present invention will now be described withreference to the accompanying drawings in which like parts have the samedesignated references and in which:

FIG. 1 is a schematic block diagram of a mobile communications network;

FIG. 2 is a schematic block diagram of part of the mobile communicationsnetwork shown in FIG. 1 illustrating a radio access interface providinga high bandwidth carrier from a first base station and a low bandwidthcarrier from a second base station contemporaneously;

FIG. 3 is a schematic block diagram of part of the mobile communicationsnetwork shown in FIG. 1 illustrating a radio access interface providinga high bandwidth carrier and a low bandwidth carrier from one basestation contemporaneously;

FIG. 4 is a schematic block diagram of part of the mobile communicationsnetwork shown in FIG. 1 illustrating a radio access interface providinga high bandwidth carrier from a radio network part according to an LTEstandard and a low bandwidth carrier from a radio network part accordingto a GPRS standard;

FIG. 5 is a schematic block diagram of part of the mobile communicationsnetwork shown in FIG. 1 illustrating a location of a load balancingentity attached to a serving gateway of the network;

FIG. 6 is a schematic block diagram of part of the mobile communicationsnetwork shown in FIG. 1 illustrating a location of a load balancingentity attached to a base station of the network;

FIG. 7 is a part schematic part function block diagram illustrating anexample operation of a load balancing entity according to an embodimentof the present technique;

FIG. 8 is a signalling flow diagram illustrating an example oftransferring a communications terminal from a high bandwidth carrier toa low bandwidth carrier when the communications terminal enters the idlemode;

FIG. 9 is a message flow diagram illustrating an example of transferringa communications terminal from a high bandwidth carrier to a lowbandwidth carrier by piggybacking transfer commands on RRC messages; and

FIG. 10 is an illustrative representation of an RRC signalling messagewhich has been adapted to include a field which provides a transferinstruction between a high bandwidth carrier and a low bandwidthcarrier.

DESCRIPTION OF EXAMPLE EMBODIMENTS

Embodiments of the present invention will now be described withreference to an implementation which uses a mobile communicationsnetwork operating in accordance with the 3GPP Long Term Evolution (LTE)standard. FIG. 1 provides an example architecture of an LTE network. Asshown in FIG. 1 and as with a conventional mobile communicationsnetwork, mobile communications terminals (also called communicationterminals or terminals) 1 are arranged to communicate data to and frombase stations 2 which are referred to in LTE as enhanced NodeBs(eNodeB), for transmitting and receiving data via the wireless or radioaccess interface with the communications terminals 1.

The base stations or eNodeB's 2 are connected to a serving gateway S-GW6 which is arranged to perform routing and management of mobilecommunications services to the communications terminals 1 as they roamthroughout the mobile communications network. In order to maintainmobility management and connectivity, a mobility management entity (MME)8 manages the enhanced packet service (EPS) connections with thecommunications terminals 1 using subscriber information stored in a homesubscriber server (HSS) 10. Other core network components include thepolicy charging and resource function (PCRF) 12 and a PDN (Packet DataNetwork) gateway (P-GW) 14 which connects to an internet network 16 andfinally to an external server 20. More information may be gathered forthe LTE architecture from the book entitled “LTE for UMTS OFDM andSC-FDMA based radio access”, Holma H. and Toskala A. page 25 ff.

In the following description LTE/SAE terminology and names are used.However embodiments of the present technique can be applied to othermobile communications systems such as UMTS and GERAN with the GSM/GPRScore network. Indeed as will be explained below in one example a lowbandwidth carrier is provided from a radio network part of a GPRSnetwork.

As shown in FIG. 1 in addition to the network elements which form partof the LTE network, the network also includes infrastructure equipmentwhich operates in accordance with the GPRS standard. As shown in FIG. 1a serving gateway support node (SGSN) 22 is connected to the MME 8 andPCRF 12. Connected to the SGSN 22 are two Node B's 24. Thus the SGSN andthe Node Bs provide a radio access network conforming to the GPRSstandard. Accordingly, the network shown in FIG. 1 forms a heterogeneousradio access network providing radio access interfaces in accordancewith different standards. As such and as will be explained in thefollowing paragraphs the GPRS network and more particularly the Node B's24 can provide a low bandwidth radio access interface, which is referredto in the following discussion as a low bandwidth carrier. In contrastthe radio access interface provided by the radio access part of the LTEnetwork which includes the eNode B's 2 and the S-GW 6 can provide in oneexample a relatively high bandwidth communications facility inaccordance with the LTE radio access interface which will be referred toin the following description as a high bandwidth carrier.

Similarly, in another example a bandwidth available to the LTE networkfor the radio access interface provided by the eNode B's 2 may bedivided into a high bandwidth carrier part and a low bandwidth carrierpart. Therefore, as will be explained shortly there are variousconfigurations for providing a high bandwidth carrier and a lowbandwidth carrier from the radio network part of a mobile communicationsnetwork. In some examples the low bandwidth carrier and the highbandwidth carrier may be provided from the same radio access interface,whereas in other examples the low bandwidth carrier may be providedusing a different radio access interface to the which provides the highbandwidth interface. In some examples, the low bandwidth carrier isconfigured to communicate small amounts of data more efficiently usingthe low bandwidth carrier which is particularly applicable to thecommunication of data from MTC-type devices.

As shown in FIG. 2 one example of the provision of a high bandwidthcarrier and a low bandwidth carrier contemporaneously to a communicationterminal (UE) 1 is shown. In FIG. 2 one of the eNode B's 2 shown in FIG.1 is provisioned with a radio access interface which can provide a highbandwidth radio access interface for communicating data to or from thecommunication terminal which is represented as a high bandwidth carrier30. However, a second eNode B 26 is shown which is configured to providea low bandwidth radio access interface for communicating low bandwidthdata which is represented as a low bandwidth carrier 32. Thus, the lowbandwidth carrier 32 is representative of a radio access interface whichhas been designed to communicate low bandwidth data such as smallamounts of delay tolerant or infrequently generated data packets moreefficiently. In addition the low bandwidth carrier may be configured foruse by communications terminals 1 having low bandwidth transmitters andreceivers for communicating data. Thus as explained above there may beclasses of devices which are provided with relatively in-expensivetransmitters and receivers which are designed to communicate on areduced bandwidth radio access interface. As such, these devices wouldbe a class of devices which would be used for low cost applications suchas for MTC devices, for which the low bandwidth carrier is provided.

As shown in FIG. 2 the high bandwidth carrier eNode B 2 and the lowbandwidth carrier eNode B 26 are both connected to the S-GW 6 andtherefore form part of the LTE network. In contrast, FIG. 3 provides anexample where both the high bandwidth carrier 30 and the low bandwidthcarrier 32 are provided from the same eNodeB 34. For the example shownin FIG. 3 the low bandwidth carrier may be formed from a partition ofcarrier frequencies of a total bandwidth available to a host radioaccess interface such as that disclosed in our co-pending UK patentapplications and referred to as a virtual carrier, which is describedbelow.

A further example is shown in FIG. 4 in which the low bandwidth carrier30 is provided by radio access part of the LTE network which includesthe eNodeB 2 and the serving gateway 6 whereas the low bandwidth carrier32 is provided by the Node B 24 and the SGSN 22 which forms part of theGPRS network shown in FIG. 1.

As explained above, the low bandwidth carrier may be provided by aseparate wireless access interface or by partitioning a part of abandwidth allocated to a host radio access interface such as in theexample of a virtual carrier. However, generally it is envisaged that alow bandwidth carrier would be available contemporaneously to acommunications terminal along with a high bandwidth carrier.Furthermore, the low bandwidth carrier could be optimised for thecommunication of infrequently generated and small amounts of data whichis delay tolerant as will be explained in the following section. Inaddition, the low bandwidth carrier may be developed to communicate onlywith communications terminals with a low bandwidth transmitter andreceiver thus providing a low cost implementation for such classes ofdevices.

Low Bandwidth Carrier/High Bandwidth Carrier

In some examples the high bandwidth carrier 30 may utilise the entirebandwidth of the radio access interface provided by the radio networkpart and the protocols of the core network part but in parallel the lowbandwidth carrier 32 may be established. The low bandwidth carrier maybe used to form a messaging network for low cost MTC-type devices. Thelow bandwidth carrier 32 may use only a part of the bandwidth of theradio network part and some reduced functionality or adapted treatmentby the core network part. As mentioned above, such a network which isdedicated to messaging is optimised for the communication of smallamounts of data. As explained above the present technique may utilise adedicated messaging network for communicating signalling type data whichis generated by, for example, application programs. The dedicatedmessaging network is therefore optimised for the communication of shortmessages such as those associated with signalling data.

In one example the low bandwidth carrier may be created from a virtualcarrier that is a carrier which exists within the complete bandwidthprovided by the radio network part of a mobile communications network.Thus in one example the low bandwidth carrier may be formed as a virtualcarrier using the techniques disclosed in our co-pending UK patentapplications numbers: 1101970.0, 1101981.7, 1101966.8, 1101983.3,1101853.8, 1101982.5, 1101980.9 and 1101972.6, the contents of which areincorporated herein by reference. However, embodiments of the presenttechnique find greater application to networks in which base stationsare deployed with a fixed bandwidth. The fixed bandwidth means that itis not easy to re-configure bandwidth allocated to the low bandwidthinterface.

The low bandwidth carrier is provided for communicating small messagesor data-grams, which can make more efficient use of hardware andcommunications resources compared with the high bandwidth carrier, andcan support a larger amount of control signalling. For example, the lowbandwidth carrier may support more physical downlink control channels(PDCCHs) per sub-frame and support a greater amount of RACH resource,which may be useful for machines that are not permanently connected tothe low bandwidth carrier, but communicate in a connectionless manner.

The high bandwidth carrier is characterized as being optimized for thetransmission of large messages at high speed. The high bandwidth carriermay have a restricted amount of available signalling resource incomparison to the amount of user-data resource.

Transmission of Small Data Messages

As explained above, smart-phones and portable computers for exampletransmit many application level signalling messages, including datarequest, keep-alive and polling type messages on a mobile communicationsnetwork. These signalling-type messages are related to certainmachine-like applications that are running on the mobile communicationsterminal. Example machine-like applications are:

-   -   An email client regularly polls the email server to check for        updates and the email server may page the email client to inform        it of pending email messages at the server. These signalling        page and poll messages are typically short (may be several        hundred bits).    -   A social networking application polls an internet server and may        be “paged” by an internet server to indicate that there is an        update to the user's social network that could be downloaded.    -   Cloud-based productivity applications may send updates to a        server in the cloud indicating whether there has been an update        to a document on the mobile communications terminal. If there is        an update, that update could be transmitted to or from the        mobile communications terminal.        Load Balancing Entity

As mentioned above, the present techniques provide an arrangement inwhich the low bandwidth carrier is used to support both MTCcommunication terminals and, when just in a low level signalling state,the high bandwidth communication terminals that would otherwise exist onthe higher bandwidth carrier.

The communications network is adapted to include a load balancing entityfor moving communication terminals from the high bandwidth carrier tothe low bandwidth carrier. The load balancing entity will transfer tothe low bandwidth carrier those communication terminals that are in astate where they are only transmitting small signalling messages. Thusconventional communications terminals which are capable of transmittingvia the high bandwidth carrier and would therefore initially camp on tothe high bandwidth carrier, would be instructed to transfer to the lowbandwidth carrier by the load balancing entity, if those communicationsterminals entered a state in which they were transmitting small amountsof data. The number of communication terminals that are transferred willdepend on the relative utilisation of both the high bandwidth carrierand the low bandwidth carrier. When the communication terminal isattached to the low bandwidth carrier and has significant data totransmit, it is transferred to the high bandwidth carrier.

There may be times where it is beneficial for legacy communicationterminals to be supported on the low bandwidth carrier. Legacycommunication terminals, such as smartphones, may engaged insignalling-type traffic. Examples of signalling type traffic areperiodic status updates, keep alive messaging, mobility measurements andcommands, tracking area updates etc.

A low bandwidth carrier that is assigned for the support of MTC trafficmay be underutilized in periods of time when there is insignificant MTCtraffic. Given that the assignment of a separate carrier is lessflexible than the assignment of a virtual carrier, this means that someof the frequency resource will be wasted at times, because it is noteasy to re-assign the frequency resources of the low bandwidth carrierto the high bandwidth carrier. Accordingly, embodiments of the presenttechnique provide a load balancing arrangement which can be used toutilize more efficiently communications resources which have beenallocated to the low bandwidth carrier.

When there are multiple carriers within the same channel bandwidth,communication terminals must choose which of the carriers to camp onto.A low bandwidth communication terminal would only choose a carrier whosebandwidth was less than or equal to its capability. However a legacycommunication terminal could camp on to either the low bandwidth carrieror the high bandwidth carrier. In this case load balancing algorithmswould be required to move legacy communication terminals between the lowbandwidth carrier and the high bandwidth carrier.

In addition load balancing algorithms may be required in order to makefull use of the low bandwidth carrier when there are few low bandwidthcommunication terminals. In this case the low bandwidth carrier could beused for both low bandwidth communication terminals and for legacycommunication terminals that are not transmitting and receivingsignificant amounts of data. Such legacy communication terminals thatare transferred to the low bandwidth carrier would suffer a higherlatency when they need to transmit and receive larger amounts of data asthey would need to be handed over to the larger bandwidth high bandwidthcarrier, with associated signalling delays.

The present technique provides for balancing a load between a lowbandwidth carrier 32 and a high bandwidth carrier 30. As explainedabove, the low bandwidth carrier is specifically designed to be adaptedto communicate data from communications terminals which have lowbandwidth transmitters and receivers. However, given that this lowbandwidth carrier is reserved for such classes of devices there may besome scenarios in which bandwidth reserved for the low bandwidth carriermay not be used by those communications terminals which are designed tocommunicate via the low bandwidth carrier 32. Accordingly, embodimentsof the present invention address a technical problem of optimising theuse of an available bandwidth for use by mobile communications networkby detecting that a communications terminal is communicating lowbandwidth type traffic such as small amounts of infrequently generateddata and moving such communications terminals onto the low bandwidthcarrier 32 when the low bandwidth carrier has capacity for communicatingsuch data.

FIGS. 5 and 6 provide two examples where a load balancing entity may belocated within the mobile communications network in order to perform aload balancing between a high bandwidth carrier 30 and a low bandwidthcarrier 32. As shown in FIG. 5 the load balancing entity 50 is attachedto the S-GW 6 whereas in the example shown in FIG. 6 the load balancingentity 50 is attached to the eNode B 2. As will be explained in thefollowing paragraphs the load balancing entity 50 is configured to movecommunications terminals from the high bandwidth carrier 30 to the lowbandwidth carrier 32 or from the low bandwidth carrier 32 to the highbandwidth carrier 30 in order to optimise use of the bandwidth reservedfor the low bandwidth carrier or furthermore to allow for more efficientuse of the high bandwidth carrier 30. The load balancing entity 50 willnow be explained.

As shown in FIG. 7 a functional representation of the operation of theload balancing entity 50 is shown to control allocation ofcommunications terminals (communication terminal) between the lowbandwidth carrier 32 and the high bandwidth carrier 30. As shown in FIG.7 in one example the low bandwidth carrier is provided with a relativelylarge amount of physical downlink control channel resource (PDCCH) inorder to grant more often requests for capacity on the uplink orallocate resources on the downlink of the low bandwidth carrier 32 whichis matched to an expected relative increase in frequency of requests forcommunicating small amounts of data from a larger number of devices. Incontrast the high bandwidth carrier 30 is provided with a relativelysmall amount of PDCCH resource which is consistent with supporting thecommunication of relatively large quantities of data.

As shown in FIG. 7 the load balancing entity 50 receives a collection ofinformation indicating a number of communications terminals (UEs) whichare currently supported on the low bandwidth carrier 52. In addition,the load balancing entity 50 also receives an indication of the trafficrequirements for the communications terminal 54. For legacycommunication terminals, there will a need to be radio resource control(RRC) handover signalling to cause the transition between the twocarriers.

Which Communication Terminals should be Moved to the Low BandwidthCarrier?

The choice of which communication terminals are load balanced to the lowbandwidth carrier may be based on:

-   -   Communication terminals that enter RRC IDLE mode may be        transferred to the low bandwidth carrier. The RRC IDLE mode        communication terminals would receive paging traffic and would        send tracking area updates (related to mobility). If there were        significant numbers of IDLE mode communication terminals, the        resulting tracking area update traffic could be significant if        the communication terminals in the cell are mobile (for example        the cell tower is next to a major road or railway). Tracking        area updates involve both uplink and downlink RRC signalling.    -   Communication terminals that are in a low activity state in RRC        CONNECTED state in the high bandwidth carrier may be put into a        discontinuous reception (DRX) mode. They may listen to the PDCCH        (in DRX mode) according to a short DRX cycle or a long DRX        cycle. If a communication terminal is put into a DRX mode, it        may be decided that such a communication terminal was in a low        activity state, but still connected state. Hence an RRC        CONNECTED communication terminal may be transferred to the low        bandwidth carrier either:    -   When it transitions to the short DRX cycle “mode”.    -   When it transitions to the long DRX cycle “mode”.    -   Inactivity timers: if no data has been passed to the        communication terminal for a certain period of time (this period        may be determined by the network operator), the communication        terminal may be sent to the low bandwidth carrier. Such an        inactivity period can be used to determine whether a        communication terminal goes into one of the DRX cycle mode.    -   Thresholds: if the data rate applied to a communication terminal        is below a certain amount, the communication terminal could be        sent to the low bandwidth carrier. This is again a method for        putting a communication terminal into one of the DRX cycle mode.        IDLE Mode Communication Terminals

As explained above, in one example the load balancing entity isconfigured to move communications terminals which enter the IDLE mode tothe low bandwidth carrier. However, once the communications terminalshave camped on to the low bandwidth carrier, the communicationsterminals may attempt to re-attach to the high bandwidth network,because the high bandwidth network is offering a better signal to noiseratio or better received carrier power. Therefore in one embodiment, thecommunications terminals are adapted to bias their attachment to the lowbandwidth carrier rather than the high bandwidth carrier. One techniquefor achieving this bias is to set a lower signal level qualityrequirement, which is termed Qrxlevmin in UMTS, for the low bandwidthinterface, when communications terminals which enter the IDLE mode aretransferred to the low bandwidth carrier. In that case IDLE modecommunication terminals would preferentially attach to the carrier withthe lower signal level quality requirements. In another example, insteadof Qrxlevmin, an offset may be specified between the signal qualitymeasurements on the high bandwidth carrier and the low bandwidthcarrier, such that the communications terminal should compare the signallevel S1 on the high bandwidth carrier with the level S1+offset on thelow bandwidth carrier: if S1=S2 and the offset is positive thencommunication terminals would preferentially move to the low bandwidthcarrier. By controlling Qrxlevmin or the offset, the proportion of IDLEmode communications terminals camped on to the low bandwidth carrier orthe high bandwidth carrier can be controlled.

In some embodiments, communications terminals may be signalled, viaSystem Information Broadcast (SIB) signalling, whether low activitycommunication terminals, such as IDLE mode communication terminals orcommunication terminals in DRX mode, should camp onto the low bandwidthcarrier or onto the high bandwidth carrier. The signalling could also beused in combination with the signal level quality method describedabove, such that those communication terminals that are in a lowactivity state and are in poorer signal conditions camp onto the lowbandwidth carrier while low activity state communication terminals inbetter signal conditions camp onto the high bandwidth carrier. This isbecause communication terminals in poorer signal conditions are morelikely to generate traffic area update signalling than communicationterminals in better signal conditions.

When a communication terminal becomes active on the low bandwidthcarrier, the network may instruct the communications terminal to handover to the high bandwidth carrier. This handover process is notcontrolled by these communication terminal measurements referred toabove, but by the load balancing entity.

Signalling Flow Diagrams for Handover Based on Transfer to IDLE Mode

FIG. 8 illustrates a signalling flow diagram for transferring acommunication terminal from a high bandwidth eNode B 2.1 to a lowbandwidth eNode B 2.2 when a transfer to IDLE mode is required.

The signalling flow illustrated in FIG. 8 is summarised below:

step name description S8.1 UE Attached to As a starting state it isassumed the mobile high BW carrier communications terminal is attachedto a high bandwidth carrier. S8.2 handover decision communicationterminal is going to drop into IDLE mode due to inactivity. Loadbalancing in high bandwidth eNode B determines that this communicationterminal should drop to the low bandwidth carrier. M8.1 handover requestbackhaul signalling from the high bandwidth eNode B to the low bandwidtheNode B indicates that the communication terminal should be transferredto the low bandwidth eNode B. This message could also indicate (in theinvention) that the communication terminal should be dropped to IDLEmode after the transfer. S8.3 admission control The low bandwidth eNodeB determines whether there is enough resource to allow the communicationterminal to be transferred to it. The determination may be based on thenumber of communication terminals that are supported on the lowbandwidth eNode B and the status of those communication terminals (forexample if there are many MTC communication terminals on the lowbandwidth carrier, admission control may fail. If there is a lot ofPRACH resource being used on the low bandwidth carrier due to H2Hcommunication terminals performing tracking area updates on the lowbandwidth carrier (e.g. from communication terminals previously loadbalanced from the high bandwidth carrier to the low bandwidth carrier),then admission control might also fail). M8.2 handover request The lowbandwidth eNode B confirms to the acknowledge high bandwidth eNode Bthat a handover will be allowed. This message, that is transferred overthe backhaul, contains a transparent container that contains the RRCreconfiguration message that the high bandwidth eNode B should send tothe communication terminal in step M8.3. M8.3 RRC the RRCreconfiguration message instructs the reconfiguration communicationterminal to transfer to the low bandwidth eNode B. This message includesdetails such as the C-RNTI (radio network temporary identifier) to beused in the new cell as well as the configuration of the new cell, suchas the PRACH configuration, PHICH configuration, maximum uplink transmitpower etc. M8.4 SN status transfer backhaul signalling transferssequence numbers from the high bandwidth eNode B to the low bandwidtheNode B for lossless PDCP transfer. S8.4 SYNC procedure communicationterminal syncs to PSS and SSS signals of the low bandwidth eNode B. S8.5RACH procedure communication terminal performs RACH procedure to attachto low bandwidth eNode B M8.5 RRC connection Part of attachmentprocedure to low bandwidth reconfiguration eNode B. complete S8.6 Pathswitch/ The MIME and serving gateway are informed modify bearer of thenew cell that the communication terminal is camped onto. S8.6 RRCconnection Signalled from the low bandwidth eNode B to release thecommunications terminal to cause the communications terminal to moveinto IDLE mode camped onto the low bandwidth eNode B.

The signalling flow shown in FIG. 8 is for a movement of acommunications terminal into the IDLE mode at the end of message M8.6.However the signalling flow presented in FIG. 8 is equally applicable tomoving to the DRX state if message M8.6 is replaced by an RRC command tomove to the DRX state. If the communications terminal is to enter theDRX state rather then the IDLE mode, either the RRC connection messageM8.6 may be replaced by an RRC command instructing the communicationsterminal to move to the DRX state or the RRC connection release commandM8.6 may be removed and an RRC command instructing the communicationsterminal to move to the DRX state may be inserted at or before messageM8.3.

The above signalling flow (in the table) can be improved in thefollowing ways:

step name improvement M8.31 RRC the message can be simplified byremoving the reconfiguration configuration of the new cell. Theconfiguration of the low BW “sister carrier” may be signalled in thehigh bandwidth carrier as part of system information. M8.32 RRC The RRCreconfiguration could be replaced by an reconfiguration RRC connectionrelease coupled with the IDLE mode load balancing means described above.This would cause the communication terminal to go into IDLE mode in thehigh bandwidth carrier and then perform a tracking update procedure inthe low bandwidth carrier. The RRC connection release message may besmaller than the RRC reconfiguration message.Signalling Flow Diagrams for Moving Between Carriers Based on DRX State

FIG. 9 shows the signalling sequence for transferring a communicationterminal that is in the DRX state from a high bandwidth eNode B 2.1 to alow bandwidth eNode B 2.2 according to an example embodiment. A messagewhich would be used to signal to the communications terminal to move tothe DRX state and to transfer to the low bandwidth carrier is shown inFIG. 10. In FIG. 10 a command message 100 is shown to include anindication to transfer to another carrier piggybacked onto a command tomove to a DRX state. This command message 102 may be used when movingfrom the high bandwidth carrier to the low bandwidth carrier which ispiggybacked onto the command message 100 to move from a DRX state. FIG.9 provides a call flow diagram illustrating a message flow controllingtransfer of a communications terminal to the low bandwidth carrier eNodeB by piggy backing transfer commands on RRC messages.

In FIG. 9 message M9.1 provides an indication of an RRC message that thecommunications terminal 1 should move to a DRX state. However, as shownin FIG. 10 in addition to the message signalling the RRC command 100 tomove to the DRX state, the message includes a field 102 indicating thatthe communications terminal should move to the low bandwidth carrier orthe higher bandwidth carrier eNode B 2.1.

In message 9.2 an RRC signal is communicated from the communicationsterminal to the eNode B 2.1 confirming the move of the communicationsterminal to the low bandwidth carrier so that the eNode B 2.2 knows thatthe communications terminal is connected to it.

In step S90 the communications terminal which is attached to the lowbandwidth eNode B enters a DRX state. In message M9.3 the low bandwidtheNode B 2.2 communicates an RRC signal to the communications terminal 1to command the communications terminal 1 to exit from the DRX state andto move to the high bandwidth carrier eNodeB.

In message M 9.4 the communications terminal communicates a message tothe high bandwidth eNode B 2.1 which confirms its move to the highbandwidth carrier.

In an alternative embodiment using a piggybacked signalling arrangement,the message M8.3 may contain a command to move to the low bandwidtheNode B 2.2 and the RRC connection release message M8.6 may be removed.

Fast Transfer Between Low and High Bandwidth Carriers in Future Releases

In some embodiments, high bandwidth communication terminals may beconfigured to transfer automatically between the high bandwidth and lowbandwidth carriers, in accordance with the following example conditions:

-   -   1. When engaged in significant activity, the communication        terminal is attached to the high bandwidth carrier.    -   2. The network signals whether communication terminals are able        to transfer to the low bandwidth carrier and provides        information about the low bandwidth carrier (for example the        exact carrier frequency, cell ID etc.). This signalling may be        relatively slow signalling such as SIB (system information)        signalling. The network may decide that communication terminals        should be able to transfer to the low bandwidth carrier if the        low bandwidth carrier is underutilized.    -   3. when a communication terminal drops into a low activity        state, it drops the connection to the high bandwidth carrier and        connects to the low bandwidth carrier. This function may be        similar to a cell selection or fast cell selection operation.

When the communication terminal is attached to the low bandwidth carrierand has significant data to transmit, it automatically transfers to thehigh bandwidth carrier by performing a cell selection to the highbandwidth carrier. SIB signalling is provided on the low bandwidth andhigh bandwidth carriers indicating that communication terminals in a lowactivity state should camp onto the low bandwidth carrier. Communicationterminals may be informed that they have been transferred to the lowbandwidth carrier for load balancing purposes and that when they havesignificant data to transmit, they should do that on the high bandwidthcarrier. Otherwise communication terminals would start transmitting thesignificant data referred to above on the low bandwidth carrier.

Various modifications may be made to the embodiments of the inventionhereinbefore described with reference to the drawings without departingfrom the scope of the present invention as expressed in the appendedclaims. Other examples are envisaged within the scope of the appendedclaims, such as where the mobile communications network operates inaccordance with a standard other than LTE. As will be appreciated alocation of a load balancing device, which is responsible fortransferring communications terminals to and from the low bandwidthcarrier, can be located at any convenient point in the network. Loadbalancing can be used to achieve various ends, such as better matchingof traffic characteristics to the type of radio access interface.

The invention claimed is:
 1. A communications terminal for communicatingdata to and receiving data from a mobile communications network, themobile communications network including a first base station, a secondbase station and a load balancer, the first base station configured toprovide a low bandwidth communications interface formed from a lowbandwidth carrier for communicating the data to or receiving the datafrom the communications terminal, and the second base station configuredto provide a high bandwidth communications interface formed from a highbandwidth carrier for communicating the data to or receiving the datafrom the communications terminal, the communications terminalcomprising: circuitry configured to: attach for communication to thehigh bandwidth communications interface provided by the second basestation according to a first radio access technology; and in response toreceiving a load balancing command from the load balancer, detach fromthe high bandwidth communications interface provided by the second basestation and re-attach to the low bandwidth communications interfaceprovided by the first base station according to the first radio accesstechnology for communicating the data to or from the mobilecommunications network via the low bandwidth communications interfacewithout checking, by the circuitry, whether the detaching and there-attaching are necessary, wherein the mobile communications networkload balancer performs a load balancing process and transmits loadbalancing commands including the load balancing command to optimizeutilization of communications resources on the low bandwidth carrier. 2.The communications terminal as claimed in claim 1, wherein the circuitryis configured to receive the load balancing command in response to firstpredetermined conditions from the mobile communications network, thefirst predetermined conditions including at least one of acharacteristic of the data communicated by the communications terminalvia the high bandwidth communications interface and a state of thecommunications terminal attached to the high bandwidth communicationsinterface.
 3. The communications terminal as claimed in claim 2, whereinthe state of the communications terminal attached to the high bandwidthcommunications interface includes whether the communications terminalenters an idle state, and consequent upon the communications terminalentering the idle state, the circuitry is configured to receive the loadbalancing command from the load balancer to detach from the highbandwidth communications interface and to re-attach to the low bandwidthcommunications interface.
 4. The communications terminal as claimed inclaim 2, wherein the state of the communications terminal attached tothe high bandwidth communications interface includes whether thecommunications terminal enters a state in which discontinuous receptionis performed, and consequent upon the communications terminal enteringthe discontinuous reception state, the circuitry is configured toreceive the load balancing command from the load balancer to detach fromthe high bandwidth communications interface and to re-attach to the lowbandwidth communications interface.
 5. The communications terminal asclaimed in claim 2, wherein the state of the communications terminalattached to the high bandwidth communications interface includes whetherthe communications terminal has not transmitted or received data for apredetermined period, and consequent upon detecting that thecommunications terminal has not transmitted or received data for thepredetermined period, the circuitry is configured to receive the loadbalancing command from the load balancer to detach from the highbandwidth communications interface and to re-attach to the low bandwidthcommunications interface.
 6. The communications terminal as claimed inclaim 2, wherein the state of the communications terminal attached tothe high bandwidth communications interface includes a rate ofcommunicating data to or receiving data from the mobile communicationsnetwork, and if the data rate falls below a predetermined amount, thecircuitry is configured to receive the load balancing command from theload balancer to detach from the high bandwidth communications interfaceand to re-attach to the low bandwidth communications interface.
 7. Thecommunications terminal as claimed in claim 1, wherein the circuitry isconfigured to receive a radio resource control message which includes anindication from the mobile communications network to detach from thehigh bandwidth communications interface and to re-attach to the lowbandwidth communications interface.
 8. The communications terminal asclaimed in claim 7, wherein the radio resource message includes a fieldindicating that the communications terminal should detach from the highbandwidth communications interface and re-attach to the low bandwidthcommunications interface.
 9. The communications terminal as claimed inclaim 1, wherein the circuitry, which is commanded to detach from thehigh bandwidth communications interface and re-attach to the lowbandwidth communications interface, is configured to receive from themobile communications network a biasing condition for re-attaching tothe high bandwidth communications interface from the low bandwidthcommunications interface to an effect that the communications terminalremains preferentially attached to the low bandwidth communicationsinterface.
 10. The communications terminal as claimed in claim 9,wherein the circuitry is further configured to: receive an indication ofan adapted received signal quality level for determining whether thecommunications terminal should detach from the low bandwidthcommunications interface and re-attach to the high bandwidthcommunications interface; compare a quality of signals received from thelow bandwidth communications interface and the high bandwidthcommunications interface; and determine whether to re-attach to the highbandwidth communications interface based on the comparison of thequality of the received signals, and the comparison of the receivedsignal quality includes the adapted received signal quality level sothat the communications terminal is biased to preferentially remainattached to the low bandwidth communications interface.
 11. Thecommunications terminal as claimed in claim 1, wherein consequent uponsecond predetermined conditions, the communications terminal re-attachesto the high bandwidth communications interface and detaches from the lowbandwidth communications interface.
 12. The communications terminal asclaimed in claim 11, wherein the second predetermined conditions includeat least one of a requirement for the communications terminal to receivedata requiring a relatively high bandwidth, a requirement for thecommunications terminal to transmit data requiring a relatively highbandwidth or a relatively high utilisation of communications resourcesof the low bandwidth communications interface by the one or morecommunications terminals which can only communicate data via the lowbandwidth communications interface.
 13. The communications terminal asclaimed in claim 1, wherein the first radio access technology operatesin accordance with a 3GPP LTE standard.
 14. A method of communicatingdata to or receiving data from a mobile communications network using acommunications terminal, the mobile communications network including afirst base station, a second base station and a load balancer, the firstbase station configured to provide a low bandwidth communicationsinterface formed from a low bandwidth carrier for communicating the datato or receiving the data from the communications terminal, and thesecond base station configured to provide a high bandwidthcommunications interface formed from a high bandwidth carrier forcommunicating the data to or receiving the data from the communicationsterminal, the method comprising: attaching the communications terminalto the high bandwidth communications interface provided by the secondbase station according to a first radio access technology forcommunicating the data; detaching, in response to receiving a loadbalancing command from the load balancer, from the high bandwidthcommunications interface provided by the second base station; andre-attaching, in response to receiving the command, to the low bandwidthcommunications interface provided by the first base station according tothe first radio access technology for communicating the data to orreceiving the data from the mobile communications network via the lowbandwidth communications interface without checking, by thecommunications terminal, whether the detaching and the re-attaching arenecessary, wherein the load balancer performs a load balancing processand transmits load balancing commands including the load balancingcommand to optimize utilization of communications resources on the lowbandwidth carrier.
 15. The method as claimed in claim 14, wherein thereceiving the load balancing command includes receiving the loadbalancing command in accordance with first predetermined conditions, thefirst predetermined conditions including at least one of acharacteristic of the data communicated by the communications terminalvia the high bandwidth communications interface and a state of thecommunications terminal attached to the high bandwidth communicationsinterface.
 16. The method as claimed in claim 15, comprising: thecommunications terminal entering an idle state, and consequent upon thecommunications terminal entering the idle state, receiving the loadbalancing command from the load balancer to detach from the highbandwidth communications interface and to re-attach to the low bandwidthcommunications interface.
 17. The method as claimed in claim 15,comprising: the communications terminal entering a state in whichdiscontinuous reception is performed, and consequent upon thecommunications terminal entering the discontinuous reception state,receiving the load balancing command from the load balancer to detachfrom the high bandwidth communications interface and to re-attach to thelow bandwidth communications interface.
 18. The method as claimed inclaim 15, wherein the state of the communications terminal attached tothe high bandwidth communications interface includes whether thecommunications terminal has not transmitted or received data for apredetermined period, and consequent upon detecting that thecommunications terminal has not transmitted or received data for thepredetermined period, receiving the load balancing command from the loadbalancer to detach from the high bandwidth communications interface andto re-attach to the low bandwidth communications interface.
 19. Themethod as claimed in claim 15, wherein the state of the communicationsterminal attached to the high bandwidth communications interfaceincludes a rate of communicating data to or receiving data from themobile communications network, and if the data rate falls below apredetermined amount, receiving the load balancing command from the loadbalancer to detach from the high bandwidth communications interface andto re-attach to the low bandwidth communications interface.
 20. Themethod as claimed in claim 14, wherein the receiving the load balancingcommand from the load balancer includes receiving a radio resourcecontrol message which includes an indication to detach from the highbandwidth communications interface and to re-attach to the low bandwidthcommunications interface.
 21. The method as claimed in claim 20, whereinthe radio resource message includes a field indicating that thecommunications terminal should detach from the high bandwidthcommunications interface and re-attach to the low bandwidthcommunications interface.
 22. The method as claimed in claim 14,comprising: receiving from the mobile communications network a biasingcondition for re-attaching to the high bandwidth communicationsinterface from the low bandwidth communications interface to an effectthat the communications terminal remains preferentially attached to thelow bandwidth communications interface.
 23. The method as claimed inclaim 22, wherein the receiving the biasing condition includes:receiving an indication of an adapted received signal quality level fordetermining whether the communications terminal should detach from thelow bandwidth; communications interface and re-attach to the highbandwidth communications interface; comparing a quality of signalsreceived from the low bandwidth communications interface and the highbandwidth communications interface; and determining whether to re-attachto the high bandwidth communications interface based on the comparisonof the quality of the received signals, wherein the comparing thequality of the received signals includes adapting the comparison inaccordance with the indication of the adapted received signal qualitylevel so that the communications terminal is biased to preferentiallyremain attached to the low bandwidth communications interface.
 24. Themethod as claimed in claim 14, comprising: consequent upon secondpredetermined conditions re-attaching to the high bandwidthcommunications interface and detaching from the low bandwidthcommunications interface.
 25. The method as claimed in claim 24, whereinthe second predetermined conditions include at least one of arequirement for the communications terminal to receive data requiring arelatively high bandwidth, a requirement for the communications terminalto transmit data requiring a relatively high bandwidth or a relativelyhigh utilisation of communications resources of the low bandwidthcommunications interface by the one or more communications terminalswhich can only communicate data via the low bandwidth communicationsinterface.
 26. The method as claimed in claim 14, wherein the firstradio access technology operates in accordance with a 3GPP LTE standard.